The present invention relates generally to slurry polishing processes for finely polishing machined or cast metal parts, and more particularly to an apparatus which controls the slurry flow during the polishing process.
The machining or casting of mechanical parts typically creates surface asperities such as tool marks, cast lines, or overall surface roughness. Certain types of machined or cast parts, such as stators and rotors used in hydrodynamic or aerodynamic applications, usually require polishing to give smooth, even surfaces before the parts can be utilized. One known polishing process involves forcing a fluid containing an extremely abrasive grit to flow over the desired part surfaces to produce finely polished surfaces. This type of polishing process, commonly known as a slurry polishing process, entails adjusting the viscosity and the abrasive loading of the slurry (fluid) to control the amount of necessary metal removal for the desired surface finish.
A slurry polishing process generally provides sufficient results when applied to simple surface shapes. However, a part having complex surface shapes and passages is not particularly suited for conventional slurry polishing because the complex surface tends to cause a nonuniform slurry flow when polished. Consequently, the nonuniform slurry flow provides inconsistent metal stock removal, i.e., excessive stock removal in certain areas of the machined or cast part, and inadequate removal in other areas.
As a consequence, metal parts having a complex surface shape have generally been hand-blended (i.e., hand grinding or sanding). Particularly complex metal parts, such as turbine rotors, typically require many tedious hours of hand blending to achieve the desired surface finish. Further, microfractures, known as alpha case microfractures, are commonly encountered due to heat build-up on the machined or cast part during the hand blending process. Alpha case microfractures are highly undesirable because of the resulting metal fatigue incurred by the polished part.